1. Field of the Invention
The present invention relates to a method of cutting a contour on an image film for cutting a masking film equal in shape to a contour of a required portion on the image film on which a picture was taken by photolithography.
2. Description of the Related Art
In the plate-making process of printed matter in which a part of a picture image is utilized, a method, in which a red-coated film, on which a transparent red coat is applied and from which only the red coat can be separated, is overlapped on an image film which is used as a manuscript and the red coat is manually cut off along the contours of a required portion to make a mask for the needless portion, is known.
However, in a case where the above described mask is manually cut off along the contour, a problem has occurred in that working efficiency and cutting accuracy are remarkably unsatisfactory.
So, the present applicant has proposed a method of mechanically cutting the mask in Japanese Patent No. 1015140 that facilitates efficient cutting of the mask with high accuracy.
According to the above described cutting method, in order to remove a needless portion of a light-permeable manuscript such as a photographic film, a locus of a light pen is used for manually tracing a contour of a required image that is detected in the form of coordinates X, Y and simultaneously, a difference of projected brightness in a direction vertical to the contour of the required image is detected by means of a group of photoelectric elements located on a table moving with the light pen to drive a data-input portion for outputting a position-detecting signal of a true contour, and an ultrasonic fine needle is used for cutting only a coat surface of the film to be processed so that the film to be processed is cut in a shape equal to the contour of the required image.
However, with the above described method, an error between the locus of the light pen manually operated and a true contour is corrected to detect a position of the true contour with a mechanism moving in both longitudinal and lateral directions and a plurality of photoelectric elements which must be mechanically operated so as to always be vertical to the contour so that a disadvantage occurs in that an apparatus for correcting the error between the locus of the light pen and the true contour is complicated.